As a representative high performance thermosetting resin, bismaleimide (BMI) resin has outstanding heat resistance, dielectric properties, wet/hot resistance and excellent mechanical properties, chemical resistance, radiation resistance, abrasion resistance and dimensional stability, so it has broad application prospects in many cutting-edge fields including aerospace, electrical insulation, new energy and so on. Unfortunately, the use of bismaleimide resin is limited to a large extent due to its inherent weaknesses such as high melting point, narrow processing window and big brittleness of cured resin. Therefore, in the past, the studies of BMI resin mainly focused on improving the processing property and toughness of BMI resin.
At present, the most often used and commercialized BMI monomer is N,N′-(4,4′-methylenediphenyl) dimaleimide (BDM), and its most effective modifiers are allyl phenyl compounds. Researches have shown that allyl compounds can modify BDM by their reactions through “Ene” and “Diels-Alder” reactions, and the modified BDM resin has improved processing property and toughness. 2-2′-Diallyl bisphenol A (DBA) is the mostly often used allyl phenyl modifier for BDM, DBA is usually synthesized from diallyl bisphenol A ether (BBE) through Claisen rearrangement, while BBE is predominantly synthesized through the reaction between bisphenol A and chloropropene or bromopropylene that is mainly derived from petroleum and coal resources. As bisphenol A has a similar structure with estrogen, so using bisphenol A during production process or daily life will increase the risks of reducing fertility as well as increasing diseases and cancers. Therefore, there is a growing demand for producing materials without bisphenol A. Meanwhile, a large amount of DBA has been used for modifying BDM, moreover, the synthesis of DBA is completely dependent on petroleum-coal resources based bisphenol A and chloropropene or bromopropylene, this does not match with the concept of green and sustainable development. Therefore, looking for a green and renewable biomass material for modifying bismaleimide resin is a task which brooks no delay.
With the rapid development of technology and industry, the materials with only high performance can't meet demand, multi-functionalization of materials has attracted great interests. For example, the flame retardancy of polymers has gained worldwide attentions in recent years. Similar as most polymers, BMI resin also has poor flame retardancy, which greatly limits its application in the high-end field.
Among the existing flame retardants for polymer materials, phosphorus-containing flame retardants have been widely used due to their low smoke, low toxicity, low corrosive and good flame retarding properties. Phosphate and phosphonate, both of which have similar properties, are the most widely used organic phosphorus flame retardants. But phosphates are mostly viscous liquids, when they are added into resins as additive flame retardants some problems such as volatility and undesirable compatibility with the resins arise. Up-to-date, no technical proposal on modifying BMI with bio-based phosphate flame retardants has been reported so far.